1. Field of the Invention
This invention relates to cordierite bodies and method of manufacture thereof, particularly of high density cordierite bodies.
2. The Prior Art
Cordierite ceramic has an extensive range of industrial applications due to its low thermal expansion coefficient, low dielectric constant, good thermal shock resistance and chemical resistivity. Ceramic parts made of cordierite are used as carriers of catalysts in automobile systems, as heat exchangers in gas turbine engines and as electronic components.
It is desirable that the cordierite ceramic be as homogeneous, dense and of low porosity as possible, to enhance its properties, including those listed above, as well as for the strength and durability of the cordierite body.
Prior art methods of manufacture of cordierite have not been satisfactory. For example, in the solid state method, one combines crystals of oxides (sized 1 to 10 micrometers) of, e.g., silica, alumina and magnesia, grinds the particles and sinters them at over 1400.degree. C., to form a nonhomogeneous ceramic which is then reground and refired in successive stages, to improve the homogeneity and density thereof in a laborious process. However, impurites are inevitably introduced with the mixing of the oxide crystals and a high degree of homogeneity and density is not realized.
U.S. Pat. No. 4,810,681 to Hayakawa (1989) discloses a similar method of manufacturing cordierite ceramics in which up to 80% by weight of cordierite crystals and up to 20% by of, e.g, a powder of zirconium oxide, are milled and mixed together, molded to form a body and then fired at over 1350.degree. C. to form a sintered body of cordierite ceramic. This is another version of the prior art solid state method, which results in a ceramic product having up to 20% impurities therein, to the detriment of the physical properties thereof noted above. Also in such process there are two phases, cordierite and zirconium oxide, which can cause structural weakness at the interfaces thereof in the ceramic end-product. Further by this method, one obtains a cordierite ceramic that has up to 6% porosity (or is 94% dense), to the detriment of the structural strength thereof.
A method for making cordierite ceramics of high homogeneity and density has therefore not been found and there is a need and market for an improved cordierite ceramic and manufacturing method therefor.
There has now been discovered a method for manufacturing cordierite ceramics of high homogeneity, high density and low porosity, to produce a new cordierite ceramic of enhanced properties and durability.